ABSTRACT
Cast polyurethane elastomers are tough, ¥exible materials designed to achieve demanding requirements not met by conventional rubbers and plastics. They consist of essentially three components:
• Diisocyanate • Polyol • Curative
CONTENTS
21.1 Introduction ........................................................................................................................ 613 21.1.1 Environmental, Health, and Safety ..................................................................... 614 21.1.2 New Materials Technology .................................................................................. 615
21.1.2.1 Isocyanates ............................................................................................... 615 21.1.2.2 Polyols ....................................................................................................... 615 21.1.2.3 Curatives ................................................................................................... 616 21.1.2.4 Prepolymers ............................................................................................. 617 21.1.2.5 One-Component Systems ...................................................................... 617 21.1.2.6 Applications ............................................................................................. 618
21.2 Polyurethanes for Roll Covering ..................................................................................... 618 21.2.1 Manufacture of Liquid Prepolymers .................................................................. 618 21.2.2 Casting of Liquid Urethane Prepolymers .......................................................... 619 21.2.3 Hard Polyurethanes for Roll Covering ............................................................... 620 21.2.4 Soft Polyurethane Roll Covering ......................................................................... 620 21.2.5 Environmental Resistance .................................................................................... 621 21.2.6 A Comparison of Polyester to Polyether Polyurethanes .................................. 621
21.3 Illustrative Patents about Sealants ................................................................................... 623 21.3.1 A-99 Used to Speed Windshield Sealant Cure with MDI and 20%
Primary Alcohol ..................................................................................................... 623 21.3.2 Bismuth Octoate Speeds Cure .............................................................................. 624 21.3.3 Breakdown of Ketimine due to Catalysis by Minor Amounts of Water ........ 625 21.3.4 Process Combining an Aldimine and Oxazolidine .......................................... 627 21.3.5 Fibers Entangle Each Other to Form a Network ............................................... 627 21.3.6 Silane-Terminated Prepolymer and Use of Clay ............................................... 629
References ..................................................................................................................................... 631
Each of these is available in a variety of chemical forms. By varying the type and ratio of these three components, the mechanical properties can be tailored over a broad range. Polyurethane cast elastomers are used in a variety of critical applications, including electrical encapsulants; abrasion-resistant linings for pumps, chutes, and conveyor belts; rollers; wiper blades; seals and gaskets; and wheels for casters, roller, and in-line skates.
